Over time, network device (e.g., router) forwarding rates have increased rapidly, whereas control plane processing capabilities have increased at a slower rate. A ratio between forwarding plane speeds and control plane speeds is very large (e.g., a factor of one-thousand or greater) and has been increasing over time. Existing methods for Internet protocol (IP) multicast are relatively control-plane intensive. One approach, known as a bit index explicit replication (BIER) forwarding method, has been introduced into the Internet Engineering Task Force (IETF) to allow many multicast groups to be simultaneously supported with minimal state in a core of a network. In the BIER forwarding method, only an ingress router for any particular packet flow needs to know which egress routers are to receive any particular packet. The BIER forwarding method does not require any explicit tree-building protocol, nor does the BIER forwarding method require intermediate routers to maintain any per-flow state. A router that implements the BIER forwarding method is known as a bit-forwarding router (BFR).
In networks that include equal cost multipath (ECMP) or link aggregation groups (LAGs) (e.g., which are becoming more common as routers get faster), the BIER forwarding method results in non-deterministic paths for any one destination. In particular, a path that a packet takes to one destination depends upon which other destinations are also receiving the same packet. Thus, in a large multicast group, if one router or a few routers are alternately joining and leaving the multicast group, the path taken to other routers in the multicast group will fluctuate, which makes network operations, administration, and management (OAM) difficult. For example, with the BIER forwarding method, it may be difficult for a trace route technique to correctly determine a path taken for a particular destination by a particular flow of packets. The BIER forwarding method may also result in inconsistent performance and/or out of order delivery of packets to any particular destination. Given that the inconsistent performance may depend upon a path taken to a particular destination, it may be difficult to diagnose such inconsistent performance.